This research plan continues the biochemical and immunological analyses of the testis-specific lactate dehydrogenase C4 isozyme (LDH-C4 lDH-X). Complete definition of this antigenic system is essential to the long-term objective of assessing the practicality and desirability of immunological contraception in human subjects. The immunological strucure and functional organization of LDH-C4will be characterized by the parallel analysis of the antibody component using hybridoma technology and the antigen component using peptide chemistry. Peptide fragments that react with antibody to LDH-C4will be used to map the antigenic surface of this protein. Small peptides will be prepared by the cleavage of LDH-C4and by chemical synthesis in order to identify antigenic domains that comprise linear sequences. Domains composed of amino acid side chains that are widely separated in the sequence but brought together by folding of the polypeptide chain will be modeled by surface simulation synthesis. This library of peptides will be used to define the precise structural specificities of the panel of monoclonal antibodies against LDH-C4. Immunization with selected peptides will generate monoclonal antibodies to particular molecular features. The fully characterized monoclonal antibodies will be used for structure-function studies of the enzymic properties of LDH-C4, for the analysis of the molecular basis of antigenic specificity of this isozyme, and for surveying the evolutionary history of LDH-C4. This immunological and biochemical analysis of LDH-C4 will provide the well-defined, biochemically characterized antigen which is essential to the long-term development of alternative technologies based on immunization procedures for contraception in human subjects.